"Light travels through space, a vacuum, at 186,282 miles per second, that is the base refractive index of 1.00, once it hits the atmosphere of earth it is slowed to 186,232 miles per second, that gives air, an index of 1.02 and in water it is slowed down to 140,061 miles per second, water has the refractive index of 1.33, if it goes through glass, such as a window pane it is slowed to 122.554 miles per second, glass has a refractive index of 1.52, when that light hits Diamond the speed is cut drastically to 77,056 miles per second, the diamond has a refractive index of 2.4175."

2.4175

Diamonds is the worlds' hardest mineral. They are transparent through a large
range of wavelengths and are commonly known as a girl's best friend. Diamonds
come in many colors, such as yellows, browns, grays, and also white, blue, black,
reddish, greenish and colorless. Diamonds are the best conductors of heat and
have a melting point of 3820 Kelvin. The crystal system/structure is isometric
and forms in such shapes as cubes and octahedrons, twinning is also seen. Depending
on how perfect the lattice of a diamond is, will change the price of a diamond.
The price can range from hundreds of dollars to hundreds of thousands of dollars.

The index of refraction of a substance is defined as n = c/v where n is the
index of refraction, c is the speed of light and v is the velocity of light
through the material. This determines the amount of refraction that occurs
when light goes from a vacuum into the material. The index of refraction of
a diamond is 2.4175, an exceptionally large number. There are no units for index
of refraction.